Brazilians in the Balkans

As said in the title, I'm brazilian, caucasian and I'm in my twenties. For the first time, I'm going to visit Serbia, Croatia, Bosnia and Montenegro, in that order. I need some help, as I'm totally lost about certain things:

• in Serbia and Bosnia is it common to local shops and comerciants try to charge us in Euro? as far as I know, Serbia and Bosnia official currency is not euro, but dinar and mark.
• We plan to cross borders by bus. Is that safe? By safe I mean: the buses are functioning well? The roads are ok? The officers of the borders and roads are negligent/corrupt and might try to take money from tourists? Are there trains to make these routes, and is it cheaper?
• As I said, our route will be Serbia, Croatia, Bosnia and Montenegro, in that order. Is that ok? Is there a shorter path?